In power supply units with a high power output which is to be distributed to several loads, it is known in the art to utilize a D.C.-A.C. converter and to provide the converter with a transformer having a plurality of secondary windings, rectifiers and series regulators being connected to the secondary windings, as in U.S. Pat. No. 4,024,451, for example. Series regulation of the output voltages results in relatively high losses, and thereby lower efficiency, as well as in the limiting of power capacity. To avoid this, three separate converters must be used for higher power level, which of course increases the weight of the power supply unit.